The values that you see are:
Penalty (tohit,todamage)
Armor class [basevalue,magicbonus]

Heavy armor is clunky and it makes fighting difficult. A mithril plate (-2,-2) [60,+24] <+5> means it has -2 to hit and damage, 60 base plus 24 magic for a total of 84 armor class, and a +5 bonus to a stat (you need to read the description to see what stat.

Any reason not to change armor info to (-1, +0) to make this more consistent with other items? Although I suppose it would be weird if you got a randart or something that offered a magical melee bonus.